1. Field of the Invention
The present invention relates to an information signal transmission system and a remote control device for the information signal transmission system and finds applications in a system of video-handling devices that are interconnected using IEEE (the Institute of Electrical and Electronics Engineers) 1394, High Performance Serial Interface Bus Standard (hereinafter simply referred to as IEEE1394). The present invention detects a recipient of information, and provides continuous information signal by switching devices in accordance with the recipient of information. For example, a program that has been enjoyed by a viewer in a living room may be continuously enjoyed by the viewer in a bed room with a simple operation. The present invention enhances ease of use in this type of network.
2. Description of the Related Art
When a diversity of video-handling devices including a television tuner, a monitor device, and an optical disk device are arranged into an audio-visual (AV) system, final output devices are typically arranged in the center of the system with the remaining devices around them mutually connected via dedicated lines.
More particularly, when the AV system is constructed of video-handling devices, video sources such as a television tuner and an optical disk device output a video signal and audio signal to a monitor device as a final output device. The monitor device is thus provided with a plurality of video input terminals and a plurality of audio input terminals, through which the video signal and audio signal are supplied by the video and audio sources.
A video-handling device such as an optical disk device having a recording capability is connected to an output terminal of a monitor device or directly to a video source such as a tuner to receive a video signal and an audio signal. In such a connection, the video-handling device transmits the video signal and audio signal over a shielded wire or a coaxial cable to reduce noise ingress.
In a camera-integrated VCR that processes a video signal in the form of digital signal, the input and output of the video signal and audio signal are performed through an interface specified by IEEE1394 Standard.
IEEE1394 Standard specifies high-speed, low-cost standard serial interface.
Transmission of Signal
According to IEEE1394, two pairs of twisted pair lines are used to transmit signals. To send a signal in one direction, the two pairs are used in a half-duplex fashion. Data is transmitted on one pair while a strobe signal is transmitted on the other pair. By exclusively OR gating both signals, a receiver side reproduces a clock.
Three data rates of 98.304 Mbps (S100), 196.608 Mbps (S200), and 393.216 Mbps (S400) are available and upward compatibility is assured in that a device of one data rate specified works on any of data rates lower than the specified data rate.
Connection of Device
Each device has up to 26 ports, and has a maximum of 63 devices connected with ports fully used. Devices are flexibly connected as long as no loop connection is used and the number of connection stages is not greater than 16.
According to IEEE1394, buses are initialized when the devices are connected, and the devices are connected in a tree structure in which one device is handled as a root device with the child and then grand child devices connected under the root device. The addresses are automatically assigned to the connected devices. In this way IEEE1394 features a large flexibility in cable connection and setting involved in connection is automatically performed.
1394 Communication
IEEE1394 allows a signal sent by one device to be relayed to another device so that the same signal is communicated to all devices within a network. More particularly, the network logically work as a buslike manner though it is electrically connected in a point-to-point manner. For this reason, each device has to arbitrate the right to use the bus prior to a start of transmission.
To get the right to use the bus, a device waits for the bus to be emptied and issues a request signal to its parent device. Upon receiving the request signal, the parent device relays it to its own parent device and the request signal thus reaches the root device. The root device returns a permission signal in response to the request signal, and the device that receives the permission signal starts communication. When a plurality of devices concurrently issue request signals, all requests except one are rejected.
Real Time Processing
In IEEE1394, a plurality of devices seeking the bus access right uses one bus on a time division multiplex basis. To transmit data, such as an audio signal and video signal, which requires real time processing, communication should be guaranteed for a certain period of time to prevent data from missing.
Data requiring real time processing is handled through transmission method called isochronous transmission. A node that manages this transmission is selected during the initialization stage of the bus. A device that transmits in isochronous transmission is assigned necessary band by the managing node. The root device transmits a cycle start packet every 125 μs, and the band-assigned device transmits an isochronous packet in succession to the cycle start packet.
In this way the band-assigned device has the chance of transmission every 125 μs. When the overall capacity of the bands used in isochronous transmission exceeds the bus capacity, band assignment cannot be performed and isochronous transmission cannot be started.
In such an IEEE1394 interface, one bus is shared by a plurality of devices on a time-division multiplex basis, and the devices are connected in a ring configuration or a star configuration to form a network. The video-handling devices are also configured in the same way.
Likewise, a network may be easily constructed in a single home. For example, a video signal reproduced by an optical disk device placed in a living room may be viewed in a monitor device in a bed room.
It would be convenient if a user could continuously watch in the bed room with an easy operation a program that has been viewed from the optical disk device in the living room.